The present invention relates to a writing control method and an image forming apparatus, and particularly to the control by which an optimum image formation can be realized corresponding to a position of a transfer sheet in the primary scanning direction.
FIG. 9 is a plan view showing an outline structure of an image forming apparatus such as a laser printer. In FIG. 9, numeral 1 is a photoreceptor drum, numeral 3 is a semiconductor laser to generate the laser light corresponding to a writing signal, numeral 4 is a polygon mirror to conduct the deflection-scanning by using the laser light, and numerals 10a and 10b are transfer sheets.
Herein, the photoreceptor drum 1 is rotated at a constant speed, and an electrostatic latent image is formed by the laser light on the surface of the photoreceptor drum 1. This electrostatic latent image is developed as a toner image by a developing unit, not shown, and the toner image is transferred onto the transfer sheet by a transfer unit, also not shown.
In this kind of image forming apparatus, when the transfer sheet is conveyed to quite the same position, the same image can be formed on the transfer sheet.
However, due to each kind of the slippage or sheet skew generated on a conveyance path from a sheet feed cassette to the photoreceptor drum, a slight slippage of position is caused.
When such the slippage or sheet skew occurs, in the conveyance direction, positioning can be conducted by a registration roller just before the transferring.
However, for the slippage or sheet skew in the direction perpendicular to the conveyance direction (primary scanning direction), it is necessary to detect the slippage of position and to change the scanning position of the laser light. In an example shown in FIG. 9, the situation of change from the state that the distance from a predetermined position is X in the transfer sheet 10a, to the state of Xxe2x80x2 in the transfer sheet 10b, is typically shown.
For such the slippage of the transfer sheet in the direction perpendicular to the conveyance direction, conventionally, the correction is conducted by oscillating a conveyance roller in the axial direction, however, the sufficient accuracy can not be obtained.
Further, in Japanese Patent Publication No. 2550558, an image forming apparatus in which the relative slippage of the transfer sheet to its ideal reference position is detected, and the position of the image formation is corrected corresponding to the slippage, is shown. Incidentally, in the image forming apparatus shown in the patent publication, the slippage of the position of the transfer sheet is detected by a plurality of light receiving elements, the plurality of detection results from the light receiving elements are connected to a ROM, and are converted into the slippage amount in the ROM.
In such the image forming apparatus, there is a problem that a large number of wiring corresponding to the resolving power is necessary between sensors and the ROM. In the actual apparatus, the sensor section is arranged on the conveyance path, however, the ROM is located on a circuit board at the remote position, therefore, there is a problem of generation of radio noise or malfunction due to external noise.
Further, because the position of the transfer sheet is detected as the relative slippage from the reference value, when the size of the transfer sheet is changed, there is also a disadvantage that this system can not cope with it, or the treatment becomes very complicate.
Accordingly, an object of the present invention is to realize a writing control method and an image forming apparatus by which, when the position of the transfer sheet is detected, the radio noise is not generated, and further, the influence of the external noise is not affected, and the image forming position is determined corresponding to the position of passage of the transfer sheet and the stable image formation can be realized.
The above object can be attained by any one of the following structures (1) to (17).
(1) In a writing control method of an image forming apparatus using a digital method, having a photoreceptor and a writing means for writing an image onto the photoreceptor, the writing control method is characterized in that a position of passage of a transfer sheet in the primary scanning direction is detected by a position detection sensor as an absolute position, and according to the detection result, the writing position is determined.
In this structure, because the position of passage of the transfer sheet in the primary scanning direction is detected by the position detection sensor as the absolute position, and according to the detection result, the writing position is determined, thereby, without depending on the passage position of the transfer sheet or the size of the transfer sheet, the stable image formation can be carried out by the determination of the accurate writing position.
(2) A digital system image forming apparatus having: the photoreceptor; a memory means for storing the supplied image data; and the writing means for writing the stored image data onto the photoreceptor as an image, the image forming apparatus is characterized in that it is provided with the position detection sensor to detect the passage position of the transfer sheet in the primary scanning direction as the absolute position, and a writing control means for determining the writing position by the writing means according to the passage position information by the position detection sensor.
In this structure, because the position of passage of the transfer sheet in the primary scanning direction is detected by the position detection sensor as the absolute position, and according to the detection result, the writing position is determined, thereby, without depending on the passage position of the transfer sheet or the size of the transfer sheet, the stable image formation can be carried out by the determination of the accurate writing position.
(3) The image forming apparatus according to the structure (2), wherein the position detection sensor is a contact type line sensor using an LED light source.
In this structure, because the position of passage of the transfer sheet in the primary scanning direction is detected as the absolute position by the position detection sensor structured by the contact type line sensor, and according to the detection result, the writing position is determined, thereby, without depending on the passage position of the transfer sheet or the size of the transfer sheet, the stable image formation can be carried out by the determination of the accurate writing position.
(4) The image forming apparatus according to the structure (3), wherein the contact type line sensor is a clock operation type contact type line sensor.
In this structure, because the position of passage of the transfer sheet in the primary scanning direction is detected as the absolute position by the position detection sensor structured by the clock operation type contact type line sensor, and according to the detection result, the writing position is determined, thereby, by counting clocks, without depending on the passage position of the transfer sheet or the size of the transfer sheet, the stable image formation can be carried out by the determination of the accurate writing position.
(5) The image forming apparatus according to the structure (4), wherein the detection resolving power of the contact type line sensor is not smaller than 0.25 mm. In other words, the detection resolving power of the contact type line sensor has a detection error of not more than 0.25 mm.
In this structure, because the detection resolving power of the contact type line sensor is not smaller than 0.25 mm, the accuracy of about 100 dpi is obtained, thereby, the stable image formation can be carried out by the determination of the accurate writing position, without depending on the passage position of the transfer sheet or the size of the transfer sheet.
(6) The image forming apparatus according to the structure (5), wherein the detection resolving power of the contact type line sensor is integer times or a reciprocal of integer times the writing resolving power.
In this structure, because the detection resolving power of the contact type line sensor is integer times or a reciprocal of integer times the writing resolving power, the accuracy proportional to the writing resolving power is obtained, therefore, a calculation necessary for determination of the writing position becomes easy, and the treatment can be simplified.
The stable image formation can be carried out by the determination of the accurate writing position, without depending on the passage position of the transfer sheet or the size of the transfer sheet.
(7) The image forming apparatus according to the structure (2), wherein a registration roller to feed the transfer sheet onto the surface of the photoreceptor is provided, and the position detection sensor is arranged on the downstream side of the registration roller.
In this structure, because the position detection sensor is arranged on the downstream side of the registration roller, the sheet skew is corrected, and the accurate writing position can be determined corresponding to the final passage position of the transfer sheet, thereby, the accurate and stable image formation can be carried out.
(8) The image forming apparatus according to the structure (7), wherein lighting of an LED light source of the contact type line sensor is in timed relationship with the driving start of the registration roller driving source.
In this structure, because lighting of the LED light source of the contact type line sensor is in timed relationship with the drive of the registration roller driving source, the passage position of the transfer sheet can be detected without uselessness, and the accurate writing position can be determined, thereby, the accurate and stable image formation can be carried out.
(9) The image forming apparatus according to the structure (3), wherein the contact type line sensor is driven by using a clock which is made to be outputted during the driving of the registration roller.
In this structure, because the lighting of the LED light source of the contact type line sensor is driven by using a clock which is made to be outputted during the driving of the registration roller, the unnecessary clock is not generated, and the stable image formation can be carried out.
(10) The image forming apparatus according to the structure (3), wherein the contact type line sensor has dimensions of a range at least to cover one end of the maximum sized transfer sheet and one end of the minimum sized transfer sheet.
In this structure, because the contact type line sensor having a range at least to cover one end of the maximum sized transfer sheet and one end of the minimum sized transfer sheet, is used, the stable image formation can be carried out by the determination of the accurate writing position, without depending on the passage position of the transfer sheet or the size of the transfer sheet.
(11) The image forming apparatus according to the structure (2), wherein a transfer sheet leading edge sensor to detect the leading edge of the transfer sheet is provided at a position at which the transfer sheet leading edge sensor is almost the same phase as the position detection sensor to the conveyance direction of the transfer sheet, and the passage position of the transfer sheet in the primary scanning direction is detected as the absolute position by the position detection sensor, after a predetermined time after the leading edge of the transfer sheet is detected by the transfer sheet leading edge sensor.
In this structure, because the passage position of the transfer sheet is detected at the predetermined timing after the leading edge of the transfer sheet is detected, the state that the transfer sheet actually passes can be accurately detected, thereby, the stable image formation can be carried out by the determination of the accurate writing position, without depending on the passage position of the transfer sheet or the size of the transfer sheet.
(12) The image forming apparatus according to the structure (3), wherein the position of the transfer sheet is detected by the position detection means comprising: a counter to count the driving clocks of the contact type line sensor; a sample hold means for holding the sensor output outputted in timed relationship with the driving clocks of the contact type line sensor; and a comparator to compare the holding result by the sample hold means to a predetermined value.
In this structure, the sensor output is held by the sample hold circuit, and compared with a predetermined value by the comparator, thereby, a stable sheet end position signal can be obtained, and the stable image formation can be carried out by determination of the accurate writing position.
(13) The image forming apparatus according to the structure (12), wherein the count stop of the counter is conducted by a point of output change of the comparator, and the stopped counter value is made a position of the transfer sheet.
In this structure, because counting of the driving clocks is stopped by the point of output change of the comparator, the state that the transfer sheet actually passes can be accurately detected, thereby, the stable image formation can be carried out by the determination of the accurate writing position.
(14) The image forming apparatus according to the structure (12), wherein the counter and the comparator are arranged in the vicinity of the contact type line sensor, and the output of the counter which is stopped by the point of the output change of the comparator is transferred to the writing control means in the serial communication.
In this structure, because the processing circuit to detect the passage position of the transfer sheet is arranged in the vicinity of the contact type line sensor, the wiring which has a possibility of generating noises, is greatly shortened. Because the output of the counter which is the detection result, is transferred in the serial communication, data can be transferred even when the number of wiring is small, and in the portion in which the wiring becomes long, a possibility of generating noises can be reduced.
(15) The image forming apparatus according to the structure (12), wherein the data of the passage position of the transfer sheet obtained by the position detection means is compared with a previously given predetermined value, and according to the comparison result, the writing position is determined.
In this structure, because the data of the passage position of the transfer sheet is compared with a predetermined value, thereby, the stable image formation can be carried out by the determination of the accurate writing position, without depending on the passage position of the transfer sheet or the size of the transfer sheet.
(16) An image writing control method of the image forming apparatus which is characterized in that: the edge position in the primary scanning direction of the recording material is detected by the position detection sensor as the absolute position; the writing position of in the primary scanning direction by the writing device is determined by defining the position of the edge position in the primary scanning direction of the recording material detected by the position detection sensor; and the writing device is controlled corresponding to the determined writing position.
Incidentally, xe2x80x9cthe writing position of in the primary scanning direction by the writing device is determined by defining the position of the edge position in the primary scanning direction of the recording material as the absolute positionxe2x80x9d implies that it is not the following: the position of the edge position of the recording material detected by the position detection sensor is compared with the reference position which is different corresponding to sizes of each recording material, and the slippage between them is found, and the writing position is determined according to the result.
(17) An image forming apparatus, which comprising: the writing device to write an image according to the image data; the control device to control the writing position in the primary scanning direction by the writing device; the conveyance device to convey the recording material; and the position detection sensor to detect the edge position of the recording material, which is conveying by the conveyance device in the primary scanning direction as the absolute position, the image forming apparatus is characterized in that: the control device determines the writing position of in the primary scanning direction by the writing device by defining the position of the edge position in the primary scanning direction of the recording material detected by the position detection sensor, and controls the writing position in the primary scanning direction of the writing device.